Unlike a primary battery, a secondary battery may be recharged. Common types of secondary batteries may be made into battery packs and used as the power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Lithium secondary batteries are suitable for portable electronic devices since they have high driving voltage and high energy density per unit weight.
Depending on the external shape, secondary batteries may be classified into different types such as square and cylindrical batteries. A cylindrical-shaped secondary battery generally includes an electrode assembly in which a positive plate and a negative plate and a separator as an insulator interposed therebetween are spiral-wound in a “jelly-roll” configuration. The electrode assembly is inserted inside a cylindrical container to form the battery.
The positive and negative plates have lead terminals, that is, conductive tabs which collect the current produced from the positive and negative plates. The conductive tab is fixed to the corresponding positive or negative plate such as by welding, to induce the current from the positive and negative plates to the positive and negative terminals of the battery.
Such a structure achieves sufficient collecting efficiency when used for a small battery with a low electric capacity. However, for a large battery that needs higher power, the area of the positive and negative plates must be increased with the increasing size of the battery, and accordingly, the resistance is increased. Therefore, the collecting efficiency for a battery using a conductive tab decreases.
In an effort to overcome these difficulties, there have been provided secondary batteries including the battery disclosed in Japanese laid-open No. 11-233148 which have plural tabs to better induce the current from each of the positive and negative plates.
Such secondary batteries can improve the collecting efficiency by fixing several lead tabs to each of the positive and negative plates to decrease the internal resistance of these batteries.
In addition, Japanese laid-open No. 6-267528 discloses a secondary battery in which a lead installing member of a long belt shape that is not coated with the active material is provided for each of the collectors of the positive and negative plates, and plural leads are welded at the lead installing member.
Such a secondary battery also has a structure such that several leads are fixed to the lead installing member. This can improve the collecting efficiency by collecting the current from the positive and negative plates with less internal resistance.
However, since the above battery requires plural leads fixed to the positive and negative electrodes, the manufacturing efficiency is low.
Furthermore, since the above batteries use spot welding to fix the lead tabs to the positive and negative plates and the collectors of the positive and negative plates are thin plates, the lead fixing regions may not maintain their shapes due to the pressure applied to the lead fixing regions, and, accordingly, it makes the welding difficult.